1. Field of the Invention
The present invention relates to a stylus abrasion detection method and surface property measurement device. Specifically, the invention relates to a stylus abrasion detection method and surface property measurement device which detect an abrasion state of a stylus in a surface property measurement device.
2. Description of Related Art
Surface property measurement devices are known which measure surface properties such as the surface roughness, the surface shape, and so on of a measured object (for example, Japanese Utility Model Application Publication No. H4-24408 and the like). Such devices bring a stylus into contact with a surface of a measured object and in this state the stylus traces along the surface of the object to be measured. According to the surface properties of the object to be measured, the stylus is displaced in a direction perpendicular to a tracing direction, and therefore it is possible to measure the surface properties of the object to be measured from the displacement amount in the position of the stylus.
In a surface property measurement device, a stylus traces along a surface of a measured object in a state where the stylus is in contact with a surface of an object to be measured, and therefore the tip of the stylus is likely to be abraded. The tip of a stylus is commonly a hemispherical shape with a diameter of approximately 2-4 μm, and therefore it is difficult to determine by visual observation the state of abrasion or chips in a stylus. When measurement is performed with the tip of the stylus abraded, the surface properties, especially the surface roughness, cannot be accurately measured, and therefore it is desirable to detect the abrasion state of a stylus and to prompt a change of stylus at the point when abrasion has reached more than a certain level.
As such, applicants have proposed a “Surface Property Measurement Device” which, first, detects the movement distance in the tracing direction of a stylus, then cumulatively stores the detected movement distance of a stylus, compares the cumulative movement distance with a set threshold value, and when the cumulative movement distance has surpassed the threshold value, prompts a change of stylus (see Japanese Patent Application No. 2010-31116).
However, even when the cumulative movement distance of the stylus is used to detect the abrasion, the abrasion state of a stylus differs according to the hardness of an object to be measured, and therefore it is not possible to accurately determine the abrasion state. In particular, when a defect such as a chip has developed in the tip of a stylus before the cumulative movement distance of the stylus reaches a threshold value, it is difficult to detect the defect.